A conventional fastening manner in sleeve-coupling type joints is a joint utilizing a rubber ring, wherein one or several rings are positioned between the ribs of a ribbed pipe or the corrugations of a corrugated pipe, for example, and the rings are pressed to the inner surface of the sleeve or pipe to be joined, the surface being formed to correspond to the profile of the rubber ring.
In addition to the rubber ring joints, ribbed pipes and corrugated pipes are also joined by welding. This is applicable especially for polyolefin pipes, which have excellent weldability properties. In the future, electric welding will be used more often. The essential feature in welding is that the temperature exceeds the melting point of plastic and that the welding pressure is sufficient. Known welding methods are disclosed for example in European patent application 531 750, U.S. Pat. No. 4,234,781 and in Finnish patent 87 685. In these methods, welding is performed by means of a welding ring placed between the pipes to be joined and electric current to be conducted to the ring. In the arrangement according to the aforementioned European reference, the required pressure is produced by moving the parts to be welded axially in relation to each other, whereas in the arrangements according to the aforementioned US and Finnish references the pressure results from the expansion of the welding ring.
However, the above-described welding manners are not applicable as such to the sleeve couplings of ribbed pipes, corrugated pipes or the like, intended for rubber ring joints, since the plastic welding ring to be tacked to the pipes to be welded cannot be placed in the space between the ribs of the ribbed pipe or the corrugations of the corrugated pipe even though this would be the best place for it in order to prevent the occurrence of detrimental axial forces in the joint. Another problem related to the welding of such light-construction pipes is that the welding pressure may deform a thin-walled pipe too much (cf. the support sleeve in Finnish patent 87 685).